Acoustic-optic ultrasonic devices using germanium containing chalcogenide glasses

ABSTRACT

Acousto-optic and ultrasonic devices are described which are dependent for their operation on certain germanium-containing compositions of the chalcogenide family of glasses. The acoustooptic devices made from these glasses exhibit high efficiencies when compared to those of devices constructed of earlier materials. The ultrasonic devices exhibit acoustic losses comparable to those of devices made from fused silica.

United States Patent Krause et al.

[151 3,655,255 1 Apr.l1,1972

[54] ACOUSTIC-OPTIC ULTRASONIC DEVICES USING GERMANIUM CONTAININGCHALCOGENIDE 1 GLASSES [72] Inventors: John Thorvald Krause, NewProvidence; Charles Robert Kurlgjian, Somerset, both of NJ.

[73] Assignee: Bell Telephone Laboratories, Incorporated,

Murray Hill, Berkeley Heights, NJ.

[22] Filed: July 13, 1970 [21] App1.No.: 54,189

[52] US Cl. ..350/1, 250/833 R, 106/47,

[51] Int. Cl. ..G02f l/34 [58] Field ofSearch ..350/16l, 1; 106/47;250/833 [56] References Cited UNITED STATES PATENTS 3,360,649 12/1967Brau et a1. ..350/1 3,370,964 2/1968 Hi1t0n,Jr.eta1 ..350/1 3,370,9652/1968 Hi1ton,Jr.eta1. ..350/1 OTHER PUBLICATIONS Walsh, T. E., lnfraredModulation Techniques," Electo-TechnoIogy, Feb. 1969, pp. 29- 33.

Savage, J. A. et al., Chalcogenide G1asses....A State of the Art Review,lnfrared Physics, Vol. 5, pp. 195- 204.

Primary Examiner-Rona1d L. Wibert Assistant ExaminerJeff RothenbergAttorney-R. J. Guenther and Edwin B. Cave [5 7] ABSTRACT Acousto-opticand ultrasonic devices are described which are dependent for theiroperation on certain germanium-containing compositions of thechalcogenide family of glasses. The acousto-optic devices made fromthese glasses exhibit high efficiencies when compared to those ofdevices constructed of earlier materials. The ultrasonic devices exhibitacoustic losses comparable to those of devices made from fused silica.

9 Claims, 10 Drawing Figures Patented April 11, 1972 4 SheetsSheet 1 mmmm J. 7. KRAUSE INVENTORS C. R. K URKJ/AN ATTORNEY Patented April 11,1972 3,655,255

4 Sheets-Sheet 3 so 40 so so 70' so 90 AS ATOMIC 7As- AV AVAVAVAVA v5AVA VWW Patented April 11, 1972 Patented A ril 11, 1972 3,555,255

4 Sheets-Sheet 4.

A AA vAvAvAvA AvAvAvAvAvA YAVAYAVAV V Se LVVWWVMVWWVV\ S b IO 20 3O 8090 ATOMIC 7o Sb A A AvAvAvAvAvA AvAvAvAvAvAvA vvvvvv BACKGROUND OF THEINVENTION l Field of the Invention This invention relates toacousto-optic devices, such as modulators, deflectors, correlators andswitches, and to acoustic devices such as ultrasonic delay lines, all ofwhich depend for their operation upon germanium-containing chalcogenideglasses.

2. Prior Art The field of communications research has for some timeincluded efforts to find glasses other than fused silica which exhibitlow acoustic losses. Such materials would be candidates for use in avariety of significant communications devices both commercial andexperimental. Examples include acoustic transmission devices such asultrasonic delay lines and the socalled acousto-optic devices such asmodulators, deflectors, correlators, switches, etc.

Of major concern for acoustic devices are glassy materials having lowacoustic loss. Glasses are generally preferred over crystallinematerials since they are invariably isotropic with respect to elasticwaves, that is, they lack crystallographic axes, thus obviating the needto orient to preferred directions. In addition, glasses are generallymore easily obtainable in large sections of optical quality than aresingle crystalline materials. No known glasses have been found toexhibit as low an acoustic loss as fused silica. Unfortunately, fusedsilica also exhibits a significant negative temperature coefficient ofdelay time, requiring for more critical applications a therrnostatedenclosure or its use with higher loss glasses or with single crystallinematerials in a composite element. The search, therefore, continues forglassy materials having both low loss and zero or near zero temperaturecoefficients of delay time.

The operation of acousto-optic devices involves altering in some wayelectromagnetic radiation traveling through the acousto-optic materialby the application of an applied acoustic signal. An importantrequirement of the acoustooptic material, in addition to its having lowacoustic loss, is a high efficiency of the acousto-optic interaction,i.e., a large portion of the total electromagnetic energy altered due toapplication of the acoustic signal.

A large number of materials have been examined in the search for highacousto-optic efficiency. See, for example, Journal of Applied Physics,Vol. 38, p. 5,149 (I967). Recent crystalline 38, which appear to beamong the most promising materials at this time, are PbMoO for use withelectromagnetic radiation of visible and near visible wavelength(described in copending application Ser. No. 82l,894, filed May 5, I969,assigned to the present assignee), and Ge, for use with infraredradiation. While each of these materials possesses acceptable values ofacoustic loss and acoustooptic efficiency, neither is sufficientlytransparent over a range broad enough to be useful with both the Nd-YAGlaser (1.06 micron) and the C0, laser 10.6 micron).

Development efforts continue to include the search for materials whichwould be suitable candidates for acoustooptic applications.

SUMMARY OF THE INVENTION The invention resides in the discovery thatcertain glass compositions are suitable for use in a wide variety ofotherwise known acousto-optic and acoustic devices. These glassesinclude ternary compositions of non-oxide chalcogenide glassesConsistent with ordinary usage, reference to the interaction of elasticwaves and electromagnetic waves generally, regardless of frequency.However, the materials of the invention impose a wavelength limit on theacousto-optic" has 5 "optic" energy, these materials being substantiallytransparent within thebandwidth of about l to 14 microns.

e ten-n acoustic is inte'iidedto include any elastic wave, includingthose within the audio, sonic, supersonic and ultrasonic frequencyranges. However, in general, acousto-optic device requirements call forthe elastic wavelength to be equal to or greater than one-half of theoptical wavelength in the acousto-optic medium.

While several typical embodiments of the two classes of devices(acoustooptic and acoustic) are described, it is to be understood thatthe materials are useful in virtually all acousto-optic and acousticapplications.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view, partlyin section, of an acousto-optic deflector utilizing one of theherein-described glass compositions as the operative element;

FIG. 2 is a diagrammatic view of a resonant acousto-optic deviceoperating as a laser mode locking structure utilizing one of theherein-described glass compositions as the operative element;

FIG. 3 is a diagrammatic view of an acoustic transmission deviceutilizing one of the herein-described glass compositions as thetransmitting medium;

FIG. 4 is a diagrammatic view of a composite acoustic transmissiondevice utilizing one of the herein-described glass compositions as oneof the elements of the acoustic transmission medium;

FIG. 5 is a ternary composition diagram showing the lowloss range ofcompositions in the system Ge-Se-As;

FIG. 6 is a diagram similar to that of FIG. 5 for the system Ge-S-As;

FIG. 7 is a diagram similar to that of FIG. 5 for the system Ge-Se-P;

FIG. 8 is a diagram Ge-S-P;

FIG. 9 is a diagram similar to that of FIG. 5 for the system Ge-Se-Sb;and

FIG. 10 is a diagram similar to that of FIG. 5 for the system Ge-S-Sb.

similar to that of FIG. 5 for the system DETAILED DESCRIPTION DevicesRefen'ing now to FIG. 1, there is shown one embodiment of a Braggdeflector consisting of an acousto-optic element 1, made of a materialherein and elastic wave source 2. Source 2 may be a piezoelectrictransducer medium, for example, of lithium niobate and in thisillustration is shown with attached electrodes 3 and 4 connected withac. or modulating source 5. Element 1 is provided with opticallypolished surfaces 6 and 7. Transparent coatings may be applied to thesesurfaces to protect them or to minimize reflection losses, or both. Inoperation, a beam 8 of electromagnetic wave energy (which may be focusedor defocused by a lens system, not shown) of a wavelength within thetransparency bandwidth of the element 1, is introduced (after beingrefracted at the surface) at some angle, 6, to the advancing elasticwave fronts diagrammatically denoted 9. While some of beam 8 continuesthrough element 1 and exits as beam 10 in the direction of beam 8, adiscrete portion is deflected by interaction with the elastic wave intoan angle 20 and emerges as beam 11.

The diagrammatic view of FIG. I illustrates the most eflicient mode ofoperation of a Bragg deflector in accordance with which the incident anddiffracted beams are at the same angle, known as the Bragg angle, to theadvancing elastic wave front. Bragg deflectors are, however, operativeover a limited range of angles centered about this optimum orientation.For

some operating conditions in which the elastic wave length isappreciably larger than the light wavelength, the difiraction angle maybe approximated as equal to the ratio of the light wavelength to theelastic wavelength. Since the elastic wavelength is inverselyproportional to the elastic frequency, the diffraction angle for a givenlight wavelength is approximately proportional to the elastic wavefrequency. Variation in this frequency therefore permits selection ofany of a variety of deflection angles. Advantage may be taken on thisrelationship in a multiposition x, y deflector system incorporating twoBragg deflectors, one for the x direction and one for the y direction.

The device of FIG. 1 may also be operated to perform the infonnationprocessing functions of pulse compression, correlation, filtering,spectrum analysis, etc., by suitably varying the frequency and/oramplitude of source 5.

Referring now to FIG. 2, there is shown an acousto-optic elementarranged for mode locking a laser. The acousto-optic element 20 isequipped with reflecting ends 21 and 22. Elastic wave transducer 23energized at the appropriate frequency by means, not shown, results in astanding elastic wave 24. Broken section 25 represents a portion of alaser cavity. Mode locking results when the acousto-optic element 20 isso designed and operated as to produce a diffraction of the sameperiodicity (or multiples thereof) as the resonant frequency whichseparates longitudinal and transverse modes of the laser.

The strength of the acousto-optic interaction may be specified in termsof an acousto-optic figure of merit:

which is related to material properties of the acousto-optic medium. Inthis expression, n is the refractive index, p is the photo-elasticconstant, v is the acoustic wave velocity (all of which depend upon thepolarizations of the optical and acoustic waves), and p is the densityof the acousto-optic medium. Values of the figure of merit have beencalculated for both longitudinal and shear elastic waves forhereindescribed compositions and have been found to compare favorablywith those for lead molybdate and germanium. Typical values of figure ofmerit (M are shown in the following table for deflection ofelectromagnetic radiation of various wavelengths (A) by these threematerials.

TABLE I PbMoO, chalcogenide Glass Germanium A 0.63 p. [.06 p. 10.6 p. M20 233 540 Appreciation of the significance of these values is aided byan understanding that the acoustic power required to deflect a givenfraction of a beam of radiation decreases with increasing figure ofmerit, but increases with increasing wavelength as the square of thewavelength. Thus, 28 times more acoustic power is required for deviceoperation at 1.06 p. than at 0.63 t, and 280 times more power isrequired at 10.6 p. than at 0.63 t. However, the higher figures of meritfor chalcogenide glasses and germanium reduce the required power for useat the longer wavelengths to the same order of magnitude as is requiredfor visible use.

Referring now to FIG. 3, there is shown one embodiment of an ultrasonicdevice in accordance with the invention, including ultrasonictransmission medium 30, piezoelectric transducers 31 and 32 attached toopposite parallel bases of medium by means of bonding layers 33 and 34,which layers also act as electrodes. Additional electrodes 35 and 36 areattached to the external bases of transducers 31 and 32. Electricalinput to and output from transducers 31 and 32 is through leads 37 and38, each attached to an electrode pair and connected to appropriatecircuitry, not shown. Delay medium 30, although depicted as having arectangular shape, may be of any shape, such as cylindrical andpolygonal, and size to give delay times consistent with the intendeddevice application. Typical delay times could be from 10 to 1,000microseconds. At least one face of the delay medium should be smooth andpreferably polished so that the input and output transducers may beaffixed thereto in such a manner as to minimize distortion of theacoustic pulses.

The transducers 31 and 32 may be any of a number of piezoelectriccrystals known to be useful for converting electric energy to acousticenergy, such as sodium, potassium niobate, lithium niobate and quartz.

It is a particular advantage of the materials herein described that theymay be fonned with relative ease into large sections of optical qualityand may therefore find use in large delay line configurations havingdelay times of the order of 1,000 microseconds.

Referring now to FIG. 4, there is shown another embodiment of anultrasonic delay line in which the delay medium is a composite structurecomprised of a material 40 of the inven tion and a second delay medium41. Such a structure is described in copending application Ser. No.601,716 filed Dec. 14, 1966, now U.S. Pat. No. 3,517,345, assigned tothe present assignee. As is pointed out in the copending application,the materials are advantageously chosen to have temperature coefficientsof delay time that are opposite in sign and lengths such that a zerotemperature coefficient results for the composite structure. In thefigure, the two sections 40 and 41 of the delay medium are shown to havelengths x and y. Electromechanical transducers 42 and 43 are electrodes44, 45, 46 and 47 and leads 48 and 49 are provided in the customarymanner. The relative lengths x and y are computed from the relationship:

adx= bd'y (2) where a and b are the absolute values of the coefficientsof delay time versus temperature and have opposite signs and d and a"are the unit delay times for the materials having their lengths definedas x and y, respectively. The total desired delay time is given bydx+dy. A suitable delay medium having a sign of delay time opposite tothat of the glasses described herein for use in the composite structureis fused silica.

GLASS COMPOSITIONS 43 Ge, 27 Se, 30 As 40 Ge, 20 Se, 40 As 25 Ge, 20 Se,55 As 25 Ge, 73 Se, 2 As 42 Ge, 56 Se, 2 As 40 Ge, 20 Se. 40 As 25 Ge,20 Se, 55 As 25 Ge, 73 Se,2As 42 Ge, 56 Se, 2 As 43 Ge, 27 Se, 30 As.

For the system Ge-S-As shown in FIG. 6, the point pairs are defined bythe following compositions in atom percent:

44 Ge, 29 S, 27 As 25 Ge, 29 S, 46 As 25 Ge, 73 S, 2 As 40 Ge, 58 S, 2As 44 Ge, 50 S, 6 As 25 Ge, 29 S, 46 As 25 Ge, 73 S, 2 As 40 Ge, 58 S, 2As 44 Ge. 50 S, 6 As 44 Ge, 29 S, 27 As.

When transmission of the electromagnetic radiation in the shortwavelength region of the transmission bandwidth of the material, forexample, 1.06 microns, is desired, compositions from the above twoternary systems containing from 2 to 5 atom percent arsenic arepreferred to minimize optic transmission losses.

For the system Ge-Se-P shown in FIG. 7, the point pairs are defined bythe following compositions in atom percent:

40 Ge, 48 Se, 12 P 33 Ge, 47 Se, 20 P 25 Ge, 52 Se, 23 P 25 Ge, 73 Se, 2P 42 Ge, 56 Se, 2 P

-- 33 Ge, 4'! Se, 20 P 25 Ge. 52 Se, 23 P 25 Ge, 73 Se, 2 P 42 Ge, 56Se, 2 P 40 Ge, 48 Se, 12 P.

For the system Ge-Se-Sb, shown in FIG. 9, the point pairs are defined bythe following compositions in atom percent:

37 Ge, 57 Se, 6 Sb 35 Ge, 52 Se, 13 Sb 25 Ge, 52 Se. 23 Sb 25 Ge, 73 Se,2 Sb 34 Ge, 64 Se, 2 Sb 35 Ge, 52 Se. 13 Sb 25 Ge, 52 Se, 23 Sb 25 Ge,73 Se, 2 Sb 34 Ge, 64 Se, 2 Sb 37 Ge, 57 Se, 6 Sb.

For the system Ge-S-Sb, shown in FIG. 10, the point pairs are defined bythe following compositions in atom percent:

35 Ge 63 S,2Sb -35 Ge,55 S, IOSb 35 Ge, 55 S, Sb 25 Ge, 55 S, Sb Ge, 55S, 20 Sb 25 Ge, 73 S, 2 Sb 25 Ge, 73 S, 2 Sb Ge, 63 S, 2 Sb.

In each of the six above-described ternary systems, the lowlosscharacteristics may be substantially retained and certain otherbeneficial effects realized by substituting up to about 50 percent byweight of So for 5a elements or 60 for 60 elements. Such substitutionsmay result in improved chemical or physical stability, and may beutilized to achieve some adjustment of working characteristics such assoftening point, as is known to those skilled in the glassmaking art.Other additives or unintended impurities such as transition elements oralkali metals, should ordinarily be kept below about 0.1 percent totalfor best results, although may be as high as 0.5 percent withoutsubstantial impairment of low-acoustic-loss characteristics. However,unwanted optical absorption bands may result. Thus, commerciallyavailable starting materials are generally suitable for use in preparingsuch glasses for delay time applications, but higher purity material maybe needed for acoustic-optic devices.

The usual methods for preparing these types of glasses are generallyknown and thus not a necessary part of this description; they aredescribed, for example, in U.S. Pat. No. 3,370,964, issued to A. R.Hilton on Feb. 27, 1968, and by A. D. Pearson in Journal ofNon-Crystalline Solids, Volume 2, Jan. 1970, p. 2.

ing the rate of decay of the received pulse echoes. Velocity wasdetermined by utilizing a refinement of the pulse superpositiontechnique. The details of this technique may be found in J. Acoust. Soc.Am. 34 609 (1962). Transducers were polished x-cut quartz plates. Inaddition to these measurements, various other properties werealsodetermined. Results are presented in Table II together with somerepresentative values for fused silica.

TABLE II Values: 33 Ge, 12 As, 55 Se Chalcogenide Fused Properties glasssilica Loss db/cm. at 500 mHz:

Shear 0.4 4.4 Longit T. l. 3. Velocity cm./sec. 10

Shea! I. 432 3. 77-} ongit 2. 518 5. 973 I.C. velocity p.p.m./ 0..

S can-.. 55 +76 Longlt 71 Density gm 4. 40 J. 203 Softening temperature(viscosity 10 p0 e) in C. 474 1, 500 Acousto-optic figure of merit (M1)164 1 Optical transmission range in microns l-l4 0. 2 5

Refractive index at 1 micron- It will be noted that acoustic velocity inthe chalcogenide glass is about one-half that in fused silica. Thus, inacoustic transmission applications requiring specific delay times, thesize of delay devices may be reduced by a factor of about two byreplacing fused silica as the delay medium with a glass composition ofthe invention. In addition, although the acoustic loss on a decibel percentimeter basis of the chalcogenide glass is about twice that of fusedsilica, due to the low acoustic velocity in the chalcogenide glass, theloss on a decibel per microsecond basis is directly comparable to thatof fused silica, the lowest-loss glassy material known.

It will also be noted from Table I that the temperature coefficients ofacoustic velocity of the chalcogenide glass and fused silica arecomparable in magnitude, but opposite in sign, making these twomaterials an excellent match for a composite ultrasonic delay line, asdescribed above. The acoustooptic figure of merit M, of 164 is seen tobe in good agreement .with the value of 233 calculated from equation(I); the high value of refractive index and low value of acousticvelocity contribute significantly to the figure of merit, as may be seenby examining equation 1 EXAMPLE 2 Several other compositions includingcompositions both from within and outside and above-described areas ofthe ternary systems were prepared in the manner described in Example land acoustic loss and acoustic velocity measured for samples from thecompositional melts. These compositions and their longitudinal loss andsome longitudinal velocity values are reported in Table 111. Los valuesfor compositions of the invention are reported at 500 megahertz, whileloss values for the remaining compositions, in general being too largefor convenient measurement at 500 MHz, are reported at 20 MHz.

TABLE III It will be seen from the table that each of the compositionsfalling within the above-described areas of the ternary diagramsexhibits values of acoustic loss and acoustic velocity comparable tothose of the composition described in Example I, which values establishthe utility of these compositions for the intended device uses.

We claim:

1. A device for modifying a beam of electromagnetic radiationcomprising: an acousto-optic material together with means forintroducing the beam thereto so that at le staportion of said beampasses through said materifi in a first I direction, andmeafisTfGYfranSmitting acoustic pulses through said material in a seconddirection substantially transverse to the beam direction, characterizedin that said acousto-optic material is a glass comprising from 25 to 44atom percent germanium, l to 5 atom percent of at least one elementselected from the group consisting of phosphorus, arsenic and antimonyand 20 to 73 atom percent of at least one element selected from thegroup consisting of sulphur and selenium.

2. The device of claim 1 in which the acousto-optic material has acomposition within an area of the ternary diagram for germanium,selenium and arsenic formed by connecting with straight lines thefollowing point pairs:

43 Ge, 27 Se, 30 As 40 Ge, 20 Se, 40 As 25 Ge, 20 Se, 55 As 25 Ge, 73Se, 2 A: 42 Ge, 56 Se, 2 A:

40 Ge, 20 Se, 40 As 25 Ge, 20 Se, 55 As 25 Ge, 73 Se, 2 Al 42 Ge, 56 Se,2 A: 43 Ge, 27 Se, 30 As.

44 Ge, 29 S, 27 As 25 Ge, 29 S, 46 As 25 Ge, 29 S, 46 As 25 Ge, 73 S, 2A:

25 Ge, 13 s, 2 A: llfce, 58 s. 2 A: 4oo=.sss,2,u -44oe,s0s,6/u 44 so s.6 A: 44 Ge, 29 s, 21 As.

5. The device of claim 4 in which the material contains from 2 to 5 atompercent of arsenic.

6. The device of claim 1 in which the acousto-optic material has acomposition within an area of the ternary diagram for germanium,selenium and phosphorus formed by connecting with straight lines thefollowing point pairs:

40 Ge, 48 Se, 12 P 33 Ge, 47 Se, 20 P 33 Ge, 47 Se, 20 P 25 Ge, 52 Se,23 P 25 Ge,52 Se,23P 25 Ge, 73 Se,2P

25 Ge, 73 Se, 2 P 42 Ge, 56 Se, 2 P

- 42 Ge, 56Se,2 P 4062,48 Se, l2 P.

7. The device of claim 1 in which the acousto-optic material has acomposition within an area of the ternary diagram for germanium, sulfurand phosphorus formed by connecting with straight lines the followingpoint pairs:

:7 Ge, 51 Se, 6 Sb as Ge, 52 Se, 13 Sb 25 Ge, 52 Se, 23 Sb :5 Ge, 13 Se,2 Sb 34 Ge, 64 Se, 2 Sb 35 Ge, 52 Se, l3 Sb 25 Ge, 52 Se. 23 Sb 25 Ge.73 Se. 2 Sb 34 Ge, 64 Se, 2 Sb 37 Ge, 57 Se, 6 Sb.

9. The device of claim 1 in which the acousto-optic material has acomposition within an area of the ternary diagram for germanium, sulfurand antimony formed by connecting with straight lines the followingpoint pairs:

35 Ge, 63 S, 2 Sb 35 Ge, 55 5, l0 Sb 25 Ge, 55 S, 20 Sb 25 Ge, 73 S, 2Sb 35 Ge, 55 S, 10 Sb 25 Ge. 55 S, 20 Sb 25 Ge, 73 S, 2 Sb 35 Ge, 63 S,2 Sb.

l l i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,655,255 Dated A ril 11, 1972 Inventor(s) John T. Krause, Charles R.Kurkjian It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

On the title page change the title from "Acoustic-Optic UltrasonicDevices Using Germanium Containing Chalcogenide Glasses" to--Acousto-Optic and Ultrasonic Devices Using Germanium ContainingChalcogenide Glasses- Column 1, line 1, change the title from"Acoustic-Optic Ultrasonic Devices Using Germanium ContainingChalcogenide Glasses" to Acousto-O'ptic and Ultrasonic Devices I UsingGermanium Containing Chalcogenide Glasses" line 47, after "crystalline"delete "38" and insert -materials-,. Column 4, line 29, after "43"change "are" to and.

Signed and sealed this 19th day of September 1972 E L) Attest:

EDWARD fidllhE'lfimlR dRe RCBER'JJ GCTSLSGHALK Attesting OfficerCommissioner of Patents FORM po'wso "0&9, USCOMM-DC scan-P09 ll-lGOVIINIINT 'IIIHIIG OFFICE III, U-3WIJI

2. The device of claim 1 in which the acousto-optic material has acomposition within an area of the ternary diagram for germanium,selenium and arsenic formed by connecting with straight lines thefollowing point pairs: 43 Ge, 27 Se, 30 As - 40 Ge, 20 Se, 40 As 40 Ge,20 Se, 40 As -25 Ge, 20 Se, 55 As 25 Ge, 20 Se, 55 As - 25 Ge, 73 Se, 2As 25 Ge, 73 Se, 2 As - 42 Ge, 56 Se, 2 As 42 Ge, 56 Se, 2 As - 43 Ge,27 Se, 30 As.
 3. The device of claim 2 in which said material containsfrom 2 to 5 atom percent of arsenic.
 4. The device of claim 1 in whichthe acousto-optic material has a composition within an area of theternary diagram for germanium, sulfur and arsenic formed by connectingwith straight lines the following point pairs: 44 Ge, 29 S, 27 As - 25Ge, 29 S, 46 As 25 Ge, 29 S, 46 As - 25 Ge, 73 S, 2 As 25 Ge, 73 S, 2As - 40 Ge, 58 S, 2 As 40 Ge, 58 S, 2 As - 44 Ge, 50 S, 6 As 44 Ge, 50S, 6 As - 44 Ge, 29 S, 27 As.
 5. The device of claim 4 in which thematerial contains from 2 to 5 atom percent of arsenic.
 6. The device ofclaim 1 in which the acousto-optic material has a composition within anarea of the ternary diagram for germanium, selenium and phosphorusformed by connecting with straight lines the following point pairs: 40Ge, 48 Se, 12 P - 33 Ge, 47 Se, 20 P 33 Ge, 47 Se, 20 P - 25 Ge, 52 Se,23 P 25 Ge, 52 Se, 23 P - 25 Ge, 73 Se, 2 P 25 Ge, 73 Se, 2 P - 42 Ge,56 Se, 2 P 42 Ge, 56 Se, 2 P - 40 Ge, 48 Se, 12 P.
 7. The device ofclaim 1 in which the acousto-optic material has a composition within anarea of the ternary diagram for germanium, sulfur and phosphorus formedby connecting with straight lines the following point pairs: 40 Ge, 54S, 6 P - 35 Ge, 55 S, 10 P 35 Ge, 55 S, 10 P - 33 Ge, 58 S, 9 P 33 Ge,58 S, 9 P - 33 Ge, 66 S, 1 P 33 Ge, 66 S, 1 P -40 Ge, 59 S, 1 P 40 Ge,59 S, 1 P - 40 Ge, 54 S, 6 P.
 8. The device of claim 1 in which theacousto-optic material has a composition within an area of the ternarydiagram for germanium, selenium and antimony formed by connecting withstraight lines the following point pairs: 37 Ge, 57 Se, 6 Sb - 35 Ge, 52Se, 13 Sb 35 Ge, 52 Se, 13 Sb -25 Ge, 52 Se, 23 Sb 25 Ge, 52 Se, 23 Sb -25 Ge, 73 Se, 2 Sb 25 Ge, 73 Se, 2 Sb - 34 Ge, 64 Se, 2 Sb 34 Ge, 64 Se,2 Sb - 37 Ge, 57 Se, 6 Sb.
 9. The device of claim 1 in which theacousto-optic material has a composition within an area of the ternarydiagram for germanium, sulfur and antimony formed by connecting withstraight lines the following point pairs: 35 Ge, 63 S, 2 Sb - 35 Ge, 55S, 10 Sb 35 Ge, 55 S, 10 Sb - 25 Ge, 55 S, 20 Sb 25 Ge, 55 S, 20 Sb - 25Ge, 73 S, 2 Sb 25 Ge, 73 S, 2 Sb - 35 Ge, 63 S, 2 Sb.